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Uniycrsity  of  California  •  Berkeley 


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ASTRONOMICAL  NOTES 


From  Bulletin  No.  5 


OF   THE 


California  Academy  of  Sciences. 


BY 


GEORGE    DAVIDSON. 


1886. 


NOTES  ON  SATURN.  73 


NOTES  ON  SATURN. 

By  Prof.  George  Davidson,  A.  M.,  Ph.  D. 

After  midnight  of  Friday,  the  13th  November,  1885,  the 
atmosphere  was  unusually  steady;  sky  clear;  no  wind;  at- 
mosphere saturated  with  aqueous  vapor;  heavy  dew  falling. 
The  satellites  of  Saturn  were  plainly  visible  with  a  moder- 
ate power  to  the  equatorial  of  6.4  inches  objective.  The 
planet  was  examined  for  nearly  two  hours  with  different 
powers,  the  best  effects  being  obtained  with  powers  of  300 
to  350  diameters;  and  the  summary  of  the  matters  of  inter- 
est is  as  follows : 

The  Encke  division  was  traced  for  120^  about  each  end 
of  the  major  axis,  leaving  only  120°  not  seen.  The  division 
was  faint  but  it  was  there,  a  little  outside  the  middle  of  the 
ring  A. 

In  the  ring  B  the  inner  part  presented  such  an  appear- 
ance in  its  delicate  shading  as  would  arise  from  a  rapid  hor- 
izontal rotary  motion  being  given  to  a  disc  of  irregularly 
distributed  and  yielding  matter.  I  could  detect  no  atmos- 
pheric unsteadiness  that  would  give  rise  to  this  phenomenon. 

The  dusky  ring  presented  equally  distinct  ansce;  on  for- 
mer occasions  I  had  been  satisfied  that  they  were  sometimes 
of  different  brightness,  and  had  endeavored  to  find  some 
law  for  this  variation.  The  dusky  ring  was  well  defined  at 
the  ansie  and  across  the  body  of  the  planet,  but  I  was  con- 
vinced that  the  limb  of  the  planet  was  visible  through  the 
dusky  ring,  very  nearly,  if  not  quite  up  to  the  inner  edge  of 
ring  B. 

The  shadow  of  the  planet  was  cast  upon  the  preceding 
side,  and  where  it  reached  the  outer  edge  of  the  ring  B,  it 
was  recurved  farther  from  the  planet  as  if  the  outer  edge  of 
B  had  a  round  moulding  above  the  general  level  of  the 
plane. 

6— Bull.  Gal.  Acad.  Sci.    U.    5,  Issued  April  23,  1886. 


74  CALIFORNIA    ACADEMY    OF    SCIENCES. 

The  markings  of  tlie  planet  were  quite  distinct.  The 
darker  color  of  the  pole  was  gradually  toned  down  until  it 
met  the  second  moderately  faint  belt  south  of  the  equator. 
The  second  belt  was  quite  dark  but  appeared  to  have  a  more 
marked  darkness  on  the  following  side  of  the  central  line, 
where  it  should  have  been  brighter  on  account  of  the  sun- 
light. Then  came  the  bright  equatorial  belt  without  mark- 
ings and  north  of  it  a  narrow  dark  band  about  half  as  broad 
as  the  trace  of  the  dusky  ring  across  the  planet,  with  a  nar- 
row dark  band  about  half  as  broad  as  the  trace  of  the  dusky 
ring  across  the  planet,  with  a  narrow  lighter  space  between 
it  and  the  edge  of  the  dusky  ring. 

January  8,  1886.  The  atmosphere  was  unsteady,  but  at 
quiet  moments  I  saw  the  Encke  division  by  using  a  power 
of  250  diameters.  Observations  made  with  the  Clark  Equa- 
torial of  G.4  inches. 

January  25,  1886.  The  atmosphere  was  wonderfully 
steady.  I  saw  the  dusky  ring  of  Saturn  with  powers  as  low 
a,s  150  diameters,  and  the  equatorial  beltings  were  beauti- 
fully sharp.  The  shape  of  the  shadow  on  the  outer  part  of 
the  B  ring  was  apparently  not  so  recurved  as  heretofore.  I 
saw  the  limbs  of  the  planet  through  the  dusky  ring  to  the 
inner  edge  of  ring  B.  I  was  able  to  follow  the  grayish  in- 
ner edge  of  the  B  ring  across  the  body  of  the  planet  and  in 
contrast  with  the  dusky  ring  below  it.  The  Encke  division 
at  the  preceding  part  of  the  ellipse  was  clearly  outside  the 
middle  of  A  ;  at  the  following  part  it  was  barely  outside  the 
middle  of  A;  no  difference  of  breadth  of  the  Cassini  divis- 
ion could  be  distinguislied  at  either  extreme. 

February  14,  1886.  Atmosphere  steady.  Carried  powers 
to  450  diameters.  The  Encke  division  clearly  exhibited; 
on  the  preceding  side  it  is  outside  the  middle  of  A,  on  the 
following  side  it  is  barely  inside  the  middle  oi  A  ;  I  carry 
it  well  down  to  the  narrow  part  of  the  ellipse.  The  dusky 
-ring  is  well  seen  and  it  seems  that  the  inner  edge  extends 
more  than  half  way  from  B  to  the  planet.    The  limbs  of  the 


NOTES    ON    SATURN.  75 

planet  are  seen  through  the  dusky  ring  and  the  inner  edge 
of  B,  I  cannot  determine  any  difference  of  brightness  be- 
tween the  preceding  and  following  parts  of   the  dusky  ring. 

I  have  watched  carefully  and  repeatedly  a  minute — ex- 
cessively minute — and  white  protuberance  on  each  side  of 
the  planet  apparently  off  the  broad  bright  equatorial  belt, 
but  really  at  the  points  where  the  faintly  dark  belt  nearest 
the  dusky  ring  disappears  at  either  limb.  This  would  seem 
to  indicate  that  this  faint  dark  belt  is  raised  above  the  gen- 
eral surface  of  the  splieroid. 

March  31,  1886.  To  this  date  I  have  not  been  able,  on 
account  of  atmospheric  conditions,  to  test  the  last  observa- 
tions of  February  14. 


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